1. Field of the Invention
The present invention relates a vehicle anti-lock brake control system comprising pumps for refluxing brake fluid to a master cylinder side and an electric motor for activating the pumps through power supply from a battery, and more particularly to an improvement in the rotation speed control of the electric motor.
2. Description of the Related Art
Conventional, vehicle anti-lock control systems as described above have been known through, for example, JP-A-11-171000.
In such conventional vehicle anti-lock brake control systems, the electric motor and pumps are set such that even when the voltage of the battery declines to the minimum operating voltage, the pumps discharge a minimum discharge volume of brake fluid which is required by the pumps when the output hydraulic pressure of the master cylinder is highest. In this conventional type of vehicle anti-lock control systems, the electric motor continues to be energized from the battery while the anti-lock brake control is being performed.
It is very rare, however, that the voltage of the battery declines to its minimum operating voltage, and while the anti-lock control is being performed normally, a high voltage of in the order of 14V is applied to the electric motor. Moreover, the electric motor is constructed such that the rotation speed thereof increases so does the applied voltage in a state in which the electric motor continues to be energized, and this means that while the anti-lock brake control is normally performed, the electric motor and pumps rotate at rotational speeds which are higher than required, and hence generate operation noise which is increased in noise level equally.
The present invention was made in view of these situations, and an object thereof is to provide a vehicle anti-lock brake control system which can reduce the operating noise level by suppressing the increase in rotational speed of the electric motor and pumps.
With a view to attaining the aforesaid object, according to a first aspect of the invention, there is provided a vehicle anti-lock brake control system comprising: a pump for refluxing brake fluid to a master cylinder side; an electric motor being activated by power supply from a battery, for driving the pump; a memory unit for memorizing as a set rotation speed a rotation speed of the electric motor for allowing a minimum required volume of brake fluid to be discharged from the pumps when the output hydraulic pressure of a master cylinder is maximum; a voltage detecting unit for detecting an applied voltage applied from the battery to the electric motor; a duty ratio determining unit for determining an energizing duty ratio for energizing the electric motor such that the electric motor is rotated at the set rotation speed memorized in the memory unit, in response to the applied voltage detected by the voltage detecting unit; and a motor control unit for duty controlling the energizing of the electric motor from the battery in accordance with the energizing duty ratio determined by the duty ratio determining unit.
According to the above construction, even when the applied voltage detected at the voltage detecting unit is high, a current supplied to the electric motor is reduced through the duty control, so that the rotation speed of the electric motor becomes the set rotation speed. Namely, the electric motor and the pumps are caused to rotate at the set rotation speed irrespective of the aforesaid applied voltage, and in the normal anti-lock brake control state where the applied voltage is high, the rotation speed of the electric motor and the pumps can be maintained relatively low to thereby reduce the operating noise. Moreover, this can help aim at saving on power used. In addition, the pulsation of the brake fluid that is refluxed to the master cylinder side is reduced by maintaining low the capacity of the pumps. This helps not only relax the kickback to the brake pedal to thereby improve the feeling of operating the brakes but also omit an orifice and a damper which are conventionally provided between the master cylinder and the pumps for relaxation of the pulsation that would otherwise remain remarkable.
According to a second aspect of the invention, there is provided a vehicle anti-lock brake control system comprising: a pump for refluxing brake fluid to a master cylinder side; an electric motor being activated by power supply from a battery, for driving the pump; a memory unit for memorizing as a set rotation speed a rotation speed of the electric motor for allowing a minimum required volume of brake fluid to be discharged from the pumps when the output hydraulic pressure of a master cylinder is maximum; a voltage detecting unit for detecting an applied voltage applied from the battery to the electric motor; a hydraulic pressure detecting unit for detecting an output hydraulic pressure from the master cylinder; a duty ratio determining unit for determining an energizing duty ratio for energizing the electric motor such that the electric motor is rotated at the set rotation speed memorized in the memory unit, in response to the applied voltage detected by the voltage detecting unit; a compensating unit for compensating for the energizing duty ratio determined at the duty ratio determining unit based on a hydraulic pressure detected at the hydraulic pressure detecting unit; and a motor control unit for duty controlling in the energizing of the electric motor from the battery in accordance with an energizing duty ratio compensated by the compensating unit.
According to the construction of the second aspect of the invention, the energizing duty ratio determined at the duty ratio determining unit is such that it is determined in response to the applied voltage in order to allow the electric motor to rotate at the set rotation speed set for allowing the minimum required volume of brake fluid to be discharged from the pumps in the state where the output hydraulic pressure of the master cylinder is highest, that is, where the load applied to the electric motor is at its maximum, and therefore, the energizing duty ratio is not the reflection of the actual output hydraulic pressure of the master cylinder. However, the energizing duty ratio determined at the duty ratio determining unit is compensated for at the compensating unit in response to the hydraulic pressure detected by the hydraulic pressure detecting unit or the hydraulic pressure actually outputted by the master cylinder, and therefore, even when the applied voltage detected by the voltage detecting unit is high, the current supplied to the electric motor is reduced through the duty control, whereby the rotation speed of the electric motor becomes the rotation speed corresponding to the output hydraulic pressure of the master cylinder. Thus, in the normal anti-lock brake control state in which the applied voltage is high, the rotation speeds of the electric motor and the pumps becomes low so as to comply with the output hydraulic pressure of the master cylinder, whereby not only can the operating noise be reduced further but also the saving on electric power can be pursued further. In addition, the pulsation of brake fluid refluxed to the master cylinder side is reduced further, whereby not only can the feeling of operating the brakes be improved further but also the orifice and the damper that are conventionally provided between the master cylinder and the pumps can be omitted.